A switching power supply is a power supply device using a switching element to convert and regulate electrical power in a power conversion device for obtaining a desired output power from an input power. Examples of the switching power supply include a DC-DC converter for converting a DC power to another DC power.
In contrast to the series regulator which dissipates Joule heat resulting from its voltage drop, the switching power supply can reduce power loss. Hence, the switching power supply can achieve high accuracy and high efficiency. With regard to the relationship between the input voltage and the output voltage, the switching power supply has circuit configurations such as step-down type, step-up type, and step-up/down type.
Now, there is a semiconductor element formed on a semiconductor substrate made of a semiconductor having a wide bandgap such as silicon carbide (SIC), gallium nitride (GaN), and diamond. Such a semiconductor element is drawing attention as having the potential to significantly break through the performance limit of Si power devices. Hence, wide bandgap semiconductor devices are highly promising also in the field of power devices. Here, the wide bandgap semiconductor refers to a semiconductor having a wider bandgap than gallium arsenide (GaAs), which has a bandgap of approximately 1.4 eV. For instance, wide bandgap semiconductors include semiconductors having a bandgap of 1.5 eV or more, such as gallium phosphide (GaP, bandgap of approximately 2.3 eV), gallium nitride (GaN, bandgap of approximately 3.4 eV), diamond (C, bandgap of approximately 5.27 eV), aluminum nitride (AlN, bandgap of approximately 5.9 eV), and silicon carbide (SiC).
Typical semiconductor elements based on wide bandgap semiconductor include a junction FET (JFET), static induction transistor (SIT), metal-semiconductor FET (metal-semiconductor field-effect transistor, MESFET), heterojunction field-effect transistor (HFET), high-electron-mobility transistor (HEMT), and accumulation FET. Currently, wide bandgap semiconductor elements in practical use typically have normally-on characteristics. However, wide bandgap semiconductor elements having normally-off characteristics can also be obtained.
Wide bandgap semiconductor elements have good features as described above. The wide bandgap semiconductor element can be used as a switching element of the switching power supply for high frequency operation above megahertz (MHz). Thus, significant downsizing of the switching power supply can be expected.